Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $121.37   10.830%   $134.5144   $134.51   $134.50   $134.50  
  Purchase #2 $58.36   9.841%   $64.1032   $64.10   $64.10   $64.10  
  Purchase #3 $242.48   12.499%   $272.7876   $272.79   $272.80   $272.80  
  Purchase #4 $196.70   7.702%   $211.8498   $211.85   $211.85   $211.80  
  Purchase #5 $181.86   12.531%   $204.6489   $204.65   $204.65   $204.60  
  Purchase #6 $100.48   11.382%   $111.9166   $111.92   $111.90   $111.90  
  Purchase #7 $139.36   3.688%   $144.4996   $144.50   $144.50   $144.50  
  7 purchase totals = $1,040.61       $1,144.3201   $1,144.32   $1,144.30   $1,144.20